Listeria is a genus of Gram-positive bacteria of the bacilli class. It contains six species, typified by L. monocytogenes, the causative agent of listeriosis, an uncommon but potentially lethal food-borne infection. L. monocytogenes is one of the most virulent food-borne pathogens. Listeriosis has been reported to be the leading cause of death among food-borne bacterial pathogens, responsible for about 2,500 illnesses and 500 deaths annually in the United States.
L. monocytogenes is commonly found in soil, stream water, sewage, plants and food. Vegetables can become contaminated with L. monocytogenes from the soil. Uncooked meats, unpasteurized milk, products made from unpasteurized milk such as certain cheeses, and processed foods commonly contain Listeria. Sufficient heating and cooking will kill Listeria, but contamination of food products can occur after cooking and before packaging. Meat processing plants, for example, producing ready-to-eat products such as deli meats and hot dogs, follow extensive sanitation policies to guard against listeria contamination.
Outbreaks of Listeria have reportedly been caused by hot dogs, deli meats, raw milk, soft-ripened cheeses, raw and cooked poultry, raw meats, ice cream, raw vegetables and raw and smoked fish. Pregnant women, the elderly and those with compromised immune systems are the most vulnerable patients. In its early stages Listeria infection is effectively treated with antibiotics such as ampicillin, ciprofloxacin and azithromycin, but it is commonly not recognized until a more advanced stage is reached. Prevention of such infections is accordingly of high importance.
Salmonella is a large genus of bacteria, many species of which can cause disease if ingested by humans. Salmonella bacteria infections are commonly termed “Salmonellosis” and are manifested by diarrhea, vomiting, fever and abdominal cramps (food poisoning). Among the human harmful Salmonella species are S. enteridis and its sub-species, S. bongori and S. typhi, the human pathogen of typhoid fever.